Add ua::Array::into_array() helper (#106)

## Description

This is a follow-up to #105 and adds a helper method that is useful when
we deal mainly with arrays of a known size (this is usually the case for
PLCs which avoid dynamic memory allocation).

Co-authored-by: Uwe Klotz <uwe.klotz@gmail.com>

CHANGELOG.md

@@ -14,6 +14,7 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 - Add `serde` serialization for `ua::Array` and `ua::Variant` with array value.
 - Add constructors `ua::Variant::scalar()` and `ua::Variant::array()`.
 - Add constructor `ua::DataValue::new()`.
+- Add helper method `ua::Array::into_array()` for conversion into native Rust array.
 
 ### Changed
 

src/ua/array.rs

@@ -266,6 +266,15 @@ impl<T: DataType> Array<T> {
         self.drain_all().collect()
     }
 
+    /// Converts the array into a native Rust array.
+    ///
+    /// This avoids cloning the contained values and moves them into the array directly. When the
+    /// number of array elements does not match, this returns `None`.
+    #[must_use]
+    pub fn into_array<const N: usize>(self) -> Option<[T; N]> {
+        <[T; N]>::try_from(self.into_vec()).ok()
+    }
+
     /// Gives up ownership and returns raw parts.
     ///
     /// The returned raw parts must be deallocated with [`UA_Array_delete()`] to prevent leaking any
@@ -399,6 +408,20 @@ mod tests {
         drop(array);
     }
 
+    #[test]
+    fn convert_array() {
+        let array = ua::Array::from_slice(&[1, 2, 3].map(ua::Byte::new));
+        let wrong: Option<[ua::Byte; 4]> = array.into_array();
+        assert!(wrong.is_none());
+
+        let array = ua::Array::from_slice(&[1, 2, 3].map(ua::Byte::new));
+        let right: Option<[ua::Byte; 3]> = array.into_array();
+        assert_eq!(
+            Some([ua::Byte::new(1), ua::Byte::new(2), ua::Byte::new(3)]),
+            right
+        );
+    }
+
     #[test]
     fn print_array() {
         let array = ua::Array::from_slice(&[1, 2, 3].map(ua::Byte::new));